Method to assess the performance of domestic ventilation systems considering the influence of uncertainties

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Method to assess the performance of domestic ventilation

systems considering the influence of uncertainties

Proefschrift

ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,

op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben, voorzitter van het College van Promoties,

in het openbaar te verdedigen op maandag 26 november 2012 om 15.00 uur

door

Zhiming Yang （（（（杨志明杨志明杨志明杨志明））））

Master of Science in Structure Engineering Shanghai Jiao Tong University, Shanghai, China

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Dit proefschrift is goedgekeurd door de promotor: Promotor Prof. ir. J.J.M Cauberg

Copromotor Dr. R.M.J. Bokel Samenstelling promotiecommissie:

Rector Magnificus, voorzitter

Prof. ir. J.J.M. Cauberg, Technische University Delft, promotor Dr. R.M.J Bokel, Technische University Delft, copromotor Prof. dr. P. Heiselberg, Aalborg University

Prof. ir. A.C.W.M. Vrouwenvelder, Technische University Delft Prof. ir. P.G. Luscuere, Technische University Delft

Prof. dr. H. Hu, Shanghai Jiao Tong University

Ir. W. de Gids, Vent Guide

IBSN: 978-94-6186-101-6 Copyright @ 2012 Zhiming Yang Yang.zhiming2007@gmail.com

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Abstract

Thesis Title: Method to assess the performance of domestic ventilation systems considering the influence of uncertainties

The ventilation system plays an important role in the indoor environment of a domestic building. A ventilation system is normally designed based on the national or regional regulations. Although ventilation systems are designed based on the same design rules, performance deviations between different ventilation systems in different houses come into existence in two ways: 1) performance differences between the same types of ventilation systems, and 2) deviations between the actual and the designed performances of a ventilation system.

Performance deviations are partly caused by uncertainties that exist in the design, construction and performance measurement stages of the ventilation systems. In order to quantify the influence of these uncertainties on the performance of a ventilation system, we aimed to develop a generally applicable assessment method. The development of this assessment method was based on several points: 1.) we focused on the air flow rate required to meet the ventilation regulations to define the assessment criteria; 2) a transient rather than a steady-state perspective was used for the assessment method; 3) the uncertainties in the whole development process of a ventilation system were investigated; 4) it was aimed at exploring how the performance of the ventilation system will be with certain specified occupant behaviour rather than at predicting how the occupant will behave; 5) different levels, i.e. scales, of assessment exist when dealing with assessment of ventilation systems, and we developed different assessment approaches for these different levels.

The main outcome of this research, i.e. the assessment method, consists of three main parts: 1) the methods used to define the assessment criteria for domestic ventilation systems; 2) the methods used to identify and estimate the uncertainties in the input parameters for calculation models used to assess domestic ventilation systems; and 3) the uncertainty quantification techniques used to analyse the uncertainties and the steps required to carry out the calculations.

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Assessment criteria

Generally, it was suggested that the assessment criteria, i.e. the performance criteria of a domestic ventilation system, should be defined based on the required performance specified in the regulations, because these systems are normally designed according to these regulations.

A review on ventilation standards in four countries was carried out. Based on this review, the generic performance parameters were defined for three main performance aspects: indoor air quality, energy consumption and comfort. Performance indicators were also given with the characteristics and appropriateness of each indicator.

Identification and estimation of uncertainties

Four aspects may influence the performance of a ventilation system: the ventilation components, building components, outdoor environment and occupants. The parameters that may contain uncertainties in each of the four aspect were first investigated, i.e. the design parameters used to describe the design and the input parameters used as input for the calculation model. Then, the methods to identify the design parameters and input parameters and the typical design parameters and input parameters for each aspect were discussed and defined.

All three stages – the design stage, construction stage and performance measurement stage – can result in uncertainties in the input parameters. The uncertainty sources which may result in the uncertainties in these three stages were investigated and five sources were defined. Next, the structure of the uncertainties in an input parameter was discussed, i.e. how these five uncertainty sources constitute the uncertainties in an input parameter.

Another issue is the scale of the assessment, i.e. the number of ventilation systems being assessed. Three levels of assessment were defined. Different levels of uncertainty data and estimation approaches for the uncertainty data should be used for different levels of assessment.

Finally, the uncertainties in the typical input parameters were discussed and estimated based on the information we found.

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Abstract III Methods to carry out the uncertainty quantification analysis

Two issues had to be addressed to carry out the uncertainty quantification analysis: 1) the uncertainty quantification techniques; and 2) the steps to prepare and pre-treat the uncertainty dataset used for uncertainty quantification analysis.

Several techniques for uncertainty propagation and sensitivity analysis were studied and compared. The Monte-Carlo simulation method coupled with Latin Hypercube Sampling was proposed to be used for conducting uncertainty propagation, while the One-Factor-at-A-Time method and the Morris Factorial Sampling method were proposed to be used for conducting the sensitivity analyses. Three main issues were discussed regarding preparation and pre-treatment of the uncertainty dataset: 1) how to prepare the calculation uncertainty datasheets ; 2) how to select the uncertainty techniques and set of uncertainties for different analysis purpose; 3) how to treat the uncertainties for different commissioning statuses.

Demonstration of the application of the assessment method

Finally the methods introduced in chapters 2, 3 and 4 were demonstrated with two case studies. These cases included two types of ventilation system: 1) a mechanical exhaust with natural supply system (MENSS); and 2) a balanced ventilation with heat recovery system (BVHRS). The case studies showed that the proposed methods can act as a framework for the assessment of the performance of a domestic ventilation system considering the influence of uncertainties.

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Samenvatting

Thesis Title: Method to assess the performance of domestic ventilation systems considering the influence of uncertainties

Het ventilatiesysteem speelt een belangrijke rol voor het binnenklimaat in een woning. Normaliter wordt een ventilatiesysteem ontworpen op basis van nationale of regionale regelgeving. Ondanks dat alle ventilatiesystemen worden ontworpen op basis van dezelfde ontwerpspecificaties bestaan er toch grote verschillen in prestatie tussen deze systemen in verschillende woningen. Hiervoor kunnen twee oorzaken aangewezen worden: 1.) verschillen in onderlinge prestatie van een bepaald type ventilatiesysteem in verschillende woningen; 2.) de afwijking van de werkelijke prestatie van de ontwerpprestatie van het ventilatiesysteem.

De prestatieafwijkingen worden ten dele veroorzaakt door de onzekerheden in de ontwerpfase, in de uitvoeringsfase en in de meetfase bij oplevering van de ventilatiesystemen. Om de invloed van deze onzekerheden op de prestatie van ventilatiesystemen te kunnen kwantificeren is binnen dit promotieonderzoek een algemeen toepasbare beoordelingsmethode ontwikkeld. Deze beoordelingsmethode is gebaseerd op een aantal uitgangspunten: 1.) de nadruk bij de ontwikkeling van het beoordelingssysteem is gelegd op de luchtstroom (luchtdebiet) zoals minimaal vereist door ventilatieregelgeving als basis voor de beoordelingscriteria; 2.) een dynamisch in plaats van stationair perspectief is gebruikt voor de beoordelingsmethode; 3.) de onzekerheden in het gehele ontwikkelingsproces van een ventilatiesysteem zijn beschouwd; 4.) doel was het onderzoeken van hoe de prestatie van het ventilatiesysteem is bij een bepaald vastgelegd bewonersgedrag en niet het voorspellen van dit bewonersgedrag zelf; 5.) aangezien er verschillende (schaal)niveaus van beoordeling bestaan, is voor elk van die niveaus een eigen beoordelingssystematiek ontwikkeld.

Het belangrijkste resultaat van dit onderzoek, de beoordelingsmethode, bestaat uit drie hoofdonderdelen: 1.) de methoden om de beoordelingscriteria voor woningventilatiesystemen te definiëren; 2.) de methoden om de onzekerheden in de invoergegevens voor rekenmodellen ter beoordeling van woningventilatiesystemen

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te identificeren en te schatten; 3.) de technieken om de onzekerheden te kwantificeren en te analyseren en de stappen om de berekeningen uit te voeren.

Beoordelingscriteria

In het algemeen hebben we aangenomen dat de beoordelingscriteria, ofwel de prestatiecriteria van een woningventilatiesysteem, gebaseerd moeten zijn op de vereiste prestatie volgens de vigerende regelgeving. Woningventilatiesystemen worden immers ook ontworpen worden op basis van deze regelgeving.

Gebaseerd op een literatuurstudie naar ventilatienormen in vier verschillende landen zijn algemene prestatieparameters gedefinieerd voor de drie belangrijkste prestatieaspecten: luchtkwaliteit, energiegebruik en comfort. Ook zijn prestatie-indicatoren ontwikkeld met bijbehorende karakteristieken en geschiktheid.

Identificatie en schatting van de onzekerheden

Vier aspecten kunnen de prestatie van een ventilatiesysteem beïnvloeden: de ventilatiecomponenten, bouwcomponenten, het buitenklimaat en de gebruiker. Allereerst hebben we voor elk aspect de parameters onderzocht die onzekerheden kunnen bevatten, ofwel de ontwerpparameters die worden gebruikt om het ontwerp te beschrijven en de invoerparameters die worden gebruikt als invoer voor het rekenmodel. Daarna hebben we de methoden gedefinieerd om de ontwerp- en invoerparameters te identificeren alvorens deze ook te beschrijven voor elk van de vier aspecten.

Alle drie de fases – de ontwerpfase, de uitvoeringsfase en de meetfase bij oplevering – kunnen leiden tot onzekerheden in de invoerparameters. In dit onderzoek zijn de bronnen van onzekerheden voor al deze fases onderzocht. Vijf bronnen zijn gedefinieerd. Vervolgens is de invloed van de onzekerheden op een invoerparameter beschreven, ofwel hoe deze vijf bronnen van onzekerheden de totale onzekerheid in een invoerparameter bepalen.

Een ander punt is de schaal van de beoordeling; verschillende aantalen ventilatiesystemen kunnen worden beoordeeld. Hiervoor zijn drie niveaus van beoordeling gedefinieerd. Verschillende onzekerheidsdata en schattingsprocedures moeten worden gebruikt naar gelang het schaalniveau van de beoordeling.

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Samenvatting VII

Tot slot, zijn de onzekerheden in de gangbare en eerder gedefinieerde invoerparameters bepaald en geschat.

Methoden om de onzekerheidskwantificatieanalyse uit te voeren

Twee zaken moesten worden bepaald om de onzekerheidskwantificatieanalyse te kunnen uitvoeren: 1) de onzekerheidskwantificatietechnieken en 2) de stappen ter voorbereiding en voorbehandeling van de datasets met onzekerheden te gebruiken voor de onzekerheidskwantificatieanalyse.

Verschillende technieken voor doorwerking van onzekerheden en voor gevoeligheidsanalyses zijn onderzocht en met elkaar vergeleken. Hieruit volgde Monte-Carlo simulatie met ‘Latin Hypercube Sampling’ als methode om de doorwerking van onzekerheden te bepalen en de ‘One-Factor-at-a-Time’ methode en de ‘Morris Factorial Sampling’ methode om gevoeligheidsanalyses uit te voeren. Vervolgens zijn drie punten nader uitgewerkt om de datasets met onzekerheden voor te bereiden en voor te behandelen: 1.) hoe de berekening van de datasets met onzekerheden voor te bereiden; 2.) hoe de onzekerheidsanalysetechnieken en sets met onzekerheden te selecteren voor verschillende analysedoeleinden; 3.) hoe de onzekerheden te behandelen voor verschillende status van de opleveringscontroles.

Demonstratie van de toepassing van de beoordelingsmethode

Tot slot is de toepassing van de methoden uit de hoofdstukken 2, 3 en 4 getoond aan de hand van twee casus. Deze casus omvatten twee typen ventilatiesystemen: 1.) mechanische afvoer met natuurlijke toevoer (MANT); en 2.) gebalanceerde ventilatie met warmteterugwinning (GVWTW). De casus hebben laten zien dat de voorgestelde methode kan dienen als een raamwerk voor de beoordeling van de prestatie van woningventilatiesystemen rekening houdend met de invloed van onzekerheden.

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Introduction

1

1.1 Background

1.1.1 Why we need a properly designed ventilation system in a domestic house

A properly designed ventilation system becomes more and more important in a modern domestic house, because maintaining good indoor air quality relies increasingly on the ventilation system. We illustrate this phenomenon below in figure 1.1.

Figure 1.1: Needs for a properly designed ventilation system

Indoor air quality is very important to the health of people. Jones (1998), Guo et al (2002), Hulin et al. (2010), and Mandin et al. (2012) all emphasise the importance

Sufficient air exchange by : - Leaky house provides enough infiltration ; - Window openings .

Better air tightness ; Infiltration is reduced ; Total air exchange is reduced . Energy

saving

Require a properly designed ventilation system .

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of the indoor air quality to human health. To maintain a good indoor air quality, sufficient indoor/ outdoor air exchange rate must be provided. In the old house, due to the fact that the house was leaky, air infiltration and simply opening windows could guarantee the air exchange required to maintain indoor air quality. Then, after the energy crisis in the 70s of the last century, people realized the importance of energy saving and reducing the energy lost due to air exchange became crucial. Thus, efforts were made to reduce uncontrolled air exchange by increasing the air tightness of houses, however, if the air exchange still relied on opening windows and infiltration, a more airtight house could not provide enough air exchange to maintain a good indoor air quality, due to the reduction in air infiltration rate. Thus, people realized that it is important to provide a sufficient, but not excessive air exchange rate, i.e. air exchange should be more controllable and efficient in the domestic setting. To achieve this goal, a properly designed ventilation system is required.

1.1.2 How do we obtain a properly designed ventilation system?

In general, two questions need be answered if one wants to achieve a well-designed ventilation system:

• How much air and where is the air flow required?

• How can we realize these air flow rates?

To answer the first question, the required performances are normally specified in the ventilation regulations, based on several local factors, such as the climate, building tradition, and occupancy and occupant behaviour. To answer the second question, the design rules for a ventilation system can be found in various regulations, codes and decrees that vary across nations.

In a word, we have to design ventilation systems based on given design rules in order to produce ventilation systems that meet the performance rules set out in national or regional regulations.

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1.2 Problem definition 3 1.2 Problem definition

1.2.1 Deviation in the practical performance of the domestic ventilation systems

Though the ventilation systems are designed based on the same design rules, performance deviations between different ventilation systems in different houses come into existence in two ways:

• the performance differences within a certain type of ventilation systems for similar houses, and

• the deviation between the practical performances and the designed values

Hasselaar (2001) claims that the exhaust systems do not work according to standards and bad design and maintenance results in the reduction of exhaust volume by approximately 50% in Dutch houses. Different claims on the performance of a ventilation system with a heat recovery unit are found, for example, the optimistic sound from Schild et al. (2003) and Dodoo et al. (2011), while the critical sound is heard by Roulet et al. (2001). In the AIVC workshop 2008, several reports from different countries showed the actual performance of the ventilation system is incompliance with the regulations (Wouters, et al. 2008; Durier, 2008).

To understand such performance deviations, we can analyse how the performance of a ventilation system in a dwelling is obtained, as shown in below figure 1.2.

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Thus, we will analyze the ventilation system performance deviations using 3 aspects, the design stage, the construction stage, and the performance measurement.

Possible reasons for performance deviation:

• Variations in the design stage. The variations in the design stage are

produced by two aspects:

o design flexibility based on the design alternatives which the designer can choose without coming into conflict with the design rules. The rational is to give the designer design flexibility.

o specification uncertainty is simply a designers’ unawareness of a specification or a missing specification. For example, when the fans are selected normally only the working point of a fan is considered, not its curve. Yet the fan curve is also relevant.

• From design to practice. The design must be realized in practice. Two

aspects can make the performance of an actual system different from the design:

o construction or realization uncertainty is generated during the construction stage of a house when putting the paper design into reality.

o dynamic and stochastic factors. Dynamic and stochastic factors are related to the assumptions made in the design stage, such as the climate. Such assumptions may differ from the actual values in practice, which will cause uncertainties.

• Measurement of the performance. The measured performances of the

ventilation system deviate from the actual performances due to inaccuracy when measuring the performance parameters or to inaccurate measurement tools.

These uncertainty sources will give rise to uncertainties in the performance measurements for a ventilation system.

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1.2 Problem definition 5 1.2.2 Addressing the influence of the uncertainties on the in use performance of a ventilation system

Addressing the influence of the uncertainties involves two issues:

• identification of the assessment (performance) criteria

• estimation and analysis of the uncertainties

Identification of the performance criteria

We will not try to create new performance criteria for domestic ventilation systems but we will try to define the adequate criteria based on the existing regulations from our perspectives. Two starting points must be addressed:

• indoor air pollutants concentrations versus air flow rate. Two types of performance criteria for the ventilation system are used:

(1) the concentration based criteria, for example, the concentration of CO2

(2) the air flow based criteria, for example, the amount of air flow per hour provided by the ventilation system

Indoor air pollutants concentrations are determined by three main factors, the performance of a ventilation system, indoor pollutant emissions and occupant use of the system. We are going to focus only on the performance of the ventilation systems, not the other two factors which are beyond the control of a designer of a ventilation system. So the air flow related required performances for a ventilation system in a domestic setting in the regulations are used as the basis for defining assessment criteria.

• static approach versus dynamic approach. In most cases, the performance of a ventilation system is measured and expressed using a static approach, but in practice, the environment changes constantly. Then, to understand the in use performance of a ventilation system, we need to measure its performance from a dynamic perspective. The assessment criteria should be defined such that they meet this dynamic approach.

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Addressing and analyzing the uncertainties

The second aspect is how to estimate the uncertainties in the development process of a domestic ventilation system and then analyze their influence. Several studies have been carried out to investigate the uncertainties found in building performance:

• The types of uncertainty sources are discussed. de Wit (2002) focuses on the modelling uncertainties in the thermal performance predictions, and Wouters et al. (2004) give a rough discussion of the scenario uncertainties related to the performance of a ventilation system. Costola et al. (2010) point out the uncertainty related to wind pressure coefficients. Yildiz et al. (2011) addresses the important design parameters for reducing building energy use.

• Uncertainty estimation and quantification techniques have also been studied. De Wit (2002) demonstrates how modelling uncertainties can be estimated using an expert judgment method, while Wouters et al. (2002) propose models for estimating the uncertainties in occupant behaviour for houses. Macdonald (2001) summarizes and compares a number of uncertainty analysis techniques.

• The recent application of uncertainty quantification techniques on the ventilation study can be found in Hyun et al. (2008), Artmann et al. (2008), Breesch and Janssens (2010) and Goethals (2011).

Several complementary and different perspectives are considered in the current thesis:

• we pay attention to the uncertainties in the whole development process of a ventilation system in a dwelling, including design, construction and the in use stage, current researches have mostly focused on the stage after the construction process.

• occupant behaviour. In most of the past studies, some researches have simply ignored occupant behaviour, while others gave prediction models for occupant behaviour. In our research, we focused on how the performance of the ventilation system will react to certain occupant behaviour rather than on predicting how the occupant will behave.

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1.2 Problem definition 7

• to date research has mostly been conducted for specific cases. A general method for identifying and estimating the uncertainties in the development process of a ventilation system will be established in current thesis.

• we pay attention to the different levels of assessment, in practice, there are three levels of assessment for domestic ventilation systems, and each level of assessment has a different assessment objective:

A. global level: the assessment concerns a set of ventilation systems within a country or a region. The number of the systems is extensive. The assessment objective of the global level of assessment is generally that: an assessment of the design regulations governing the design of ventilation systems in a country or in a region, i.e. whether the design regulations provide sufficient or adequate guidance to achieve the wanted performance of the ventilation systems.

B. project level: the assessment concerns a set of ventilation systems within a housing project. The number of systems is much smaller than that of the global level. The assessment objective of the project level assessment is generally that: the overall quality of a set of designs of the ventilation systems.

C. design level: the assessment concerns one ventilation system in the design stage. The assessment objective of the design level assessment is generally that: optimization of the design of a ventilation system.

There are different consideration and treatment methods for the uncertainties for different levels of assessment which will be discussed in this research.

1.3 Research objective and research questions 1.3.1 Research objective

Based on the considerations introduced above, the research objective was defined as:

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• to establishing a generally applicable assessment method for assessment of the performance of ventilation systems in domestic dwellings, taking into consideration the uncertainties which may exist in the development process of the ventilation systems in dwellings.

1.3.2 Research questions

The assessment method was structured as shown in the figure 2.3.

Figure 1.3. Structure of the assessment method The following main and sub research questions are to be answered:

• main question 1: How to define the assessment criteria? Sub questions:

(1) In which aspects should the assessment criteria be defined? (2) How to identify the performance parameters?

(3) How to identify the performance indicators?

• main question 2: How to identify and estimate the uncertainties? Sub questions:

(1) What are the uncertainty sources?

(2) In which parameters there are uncertainties? (3) How to estimate such uncertainties?

• main question 3: How to address the influence of the uncertainties? Sub questions:

(1) What are the uncertainty quantification techniques to be used to address the overall influence of the uncertainties on the outputs and the influential parameters?

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1.4 Research approaches and structure 9

1.4 Research approaches and structure

The method for determining the assessment criteria for ventilation system is discussed in chapter 2. The methods for determining performance parameters and performance indicators are discussed.

After defining the assessment criteria, in chapter 3, the methods for identifying the uncertainties during the development of ventilation system in dwellings is investigated.

The method for dealing with the uncertainties and carrying out the uncertainty quantification analysis are studied and introduced in chapter 4.

The application of the methods introduced in chapter 2, 3 and 4 are demonstrated by one case study in chapter 5.

A guideline, which acts as an quick access to the proposed assessment method, is given in chapter 6.

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Assessment criteria

2

2.1 Introduction

In order to establish an assessment method that can be used to assess a domestic ventilation system, the assessment criteria, i.e. the performance criteria used to describe the required performance of a domestic ventilation system, should be defined first. In this chapter, the method used to define the assessment criteria is introduced.

2.2 Performance aspects related to a ventilation system

In chapter 1, it is explained that, in general, the assessment objectives for a domestic ventilation system are:

• the ability of the ventilation system to fulfill the required performance, which is air flow related, defined in the regulations

• the reaction of the ventilation system to certain occupant behavior, i.e. how the air flow behavior provided by the ventilation system is influenced by the occupant behavior

The general functions which are normally required for the performance of a domestic ventilation system were investigated and found to be related to:

• indoor air quality

• energy use

• comfort

Each of these aspects may impose a certain required performance on the ventilation system in dwellings. Below, we will shortly explain why these aspects are

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important and how they may be considered as part of the required performance for a domestic ventilation system.

Maintaining acceptable indoor air quality

Maintaining acceptable indoor air quality from a hygiene perspective is the most important and the original reason to have one ventilation system in a dwelling. The problem of indoor air quality is caused by the concentration rates of indoor pollutants generated by humans, pets, indoor activities and materials used in building materials and furnishings etc. Thus, the basic idea is to provide fresh air from outdoor air or purified air to replace the indoor air and therefore, remove/ dilute the indoor air pollutants. The generation of indoor air pollutants and their removal in shown in figure 2.1 below. Domestic ventilation systems were originally designed for this purpose.

Figure 2.1: Removing indoor air pollutant by ventilation (NEN 15665) The important performance aspects are related to:

• removing/diluting the indoor air pollutants in a certain space by providing enough air flow capacity to refresh the indoor air

• avoiding internal redistribution of pollutants by avoiding an unwanted air flow direction from polluted spaces to non-polluted spaces in a home

Pollution source Indoor air

Occupants Polluted indoor air

Health effect Health risk Outdoor air Acceptable IAQ Ventilation Exposure To certain level of concentration Remove indoor pollution

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2.2 Performance aspects related to a ventilation system 13

Energy consumption related to air exchange

Generally speaking, the energy use related to a domestic ventilation system, can be divided into two parts: heat/energy lost due to air exchange, because of indoor-outdoor temperature differences, and energy that is used to drive a ventilation system, mainly energy used to run fans , as shown in figure 2.2.

Figure 2.2: Energy consumption related to air exchange

Comfort issues

The issue of comfort has a direct influence on the user or occupants’ behavior related to a ventilation system. The following 3 performance aspects are influential aspects for a domestic ventilation system:

• draught

• acoustic noise level

• individual controllability

Draughts are normally reported in ventilation systems with an unconditioned air supply during cold weather. In practice, the draught problem can be minimized by carefully design of air inlet locations and/ or preconditioning the internal supply air.

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Aerodynamic noise is generated in a ducted ventilation system, from the ducts, grilles and fans. In order to restrict the noise in a ventilation system, design requirements may be imposed on the ventilation design in terms of maximum air velocity in a duct, minimum duct diameter and maximum noise levels for fans. In current research, we considered the draught and acoustic problems to be limitations on a ventilation system design rather than direct performance requirements. Thus we did not consider these two aspects in our assessment criteria for a domestic ventilation system.

Individual controllability of a system was specifically defined by us to be a criterion for the current research: whether the occupants of a house are free to control their individual environments without having an unwanted influence on the air flows in the other rooms.

Summary

We introduced 5 performance aspects for a domestic ventilation system in current research:

• air flow capacity

• air flow direction

• energy lost due to air exchange

• energy use used by fan(s)

• individual controllability

The appropriate performance parameters must be defined for the assessment for each of these five performance aspects. There are generally different performance parameters in different countries, but there are similarities and common elements in these performance parameters. So in the text below, a review of the ventilation regulations in different countries is given first. Then, based on an analysis of the required performance in these regulations, the key elements for defining a performance parameter will be outlined. Finally, a generic set of performance parameters for a domestic ventilation system is given.

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2.3 Performance parameters related to indoor air quality 15 2.3 Performance parameters related to indoor air quality

We reviewed the required performances for a domestic ventilation system related to indoor air quality as set out in the housing regulations in 4 countries, Canada (CA), Denmark (DK), the Netherlands (NL) and the United Kingdom (UK). We also used the works from Dorer and Breer (1998), Mcwilliams and Shearman (2005) as references.

2.3.1 Reviewing the required performance in existing regulations

The standards and building regulations for the design and required performance for a domestic ventilation system in 4 countries, CA, DK, NL and UK, were studied. Our review of these regulations and standards focused on the part for new houses. These were:

• Canadian: Residential Mechanical Ventilation System CAN/CSA-F326-M91; and the Canadian National Building Code 1995

• Danish: The 2010 Danish Building Regulations

• Dutch: Bouwbesluit 2003, and NEN 1087 (2001) Ventilation in buildings- Determination methods for new estates, and the NPR 1088 (1999) ventilation in dwellings and residential buildings – Indications for and examples of the construction of ventilation systems

• British: The Building Regulation 2010 Approved Document F: F1 Means of ventilation

In general, the required performance related to indoor air quality in the existing regulations and standards could be condensed into the following aspects:

a. required ventilation capacity b. exhaust/ supply

c. room/ house level ventilation rates

d. supply air quality: overflow and recirculation e. infiltration

f. purge ventilation g. air flow direction h. supply air distribution

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Each of these aspects will be explained below.

a. required air flow rate/ ventilation capacity

The minimum required air flow rates for the whole house and each room for the 4 countries are summarized in table 2.1.

Table 2.1: Minimum ventilation air flow rates requirements in CA, DK, NL and UK Countries/ standard reference Whole house ventilation rates Living room

Bedroom Kitchen Bathroom WC

Netherlands/ Bouwbesluit

2003

Not less than the highest value of the total exhaust flow rate and the required air flow of the largest occupation area 0.9 l/s per m2 (at least 7 l/s) 0.9 l/s per m2 (at least 7 l/s) at least 21 l/s at least 14 l/s at least 7 l/s UK/ Building reg. 2010. App. Doc. F 13 + 4(n-1) l/s (n is the number of bedroom) and no less than 0.3 l/s per m2 of internal

floor area for default occupancy (otherwise 4 l/s

for per extra occupant) Intermittent rate: no less than 30 l/s adjacent to hob; or 60 l/s elsewhere; Continuous rate: no less than 13 l/s Intermittent rate: no less than 15 l/s; Continuous rate: no less than 8 l/s no less than 6 l/s Canada/ CSA/CAN-F326 or Canadian National Bui. Code 1995 no less than 0.3 ach and 5 l/s, equal to sum of individual rooms rates no less than 5 l/s no less than master bed. 10 l/s; other bed. 5 l/s Inter. 50l l/s; Cont. 30 l/s inter. 25 l/s; cont. 15 l/s no less than 5 l/s Denmark/ The 2011 Danish Building Regulations no less than 0.3 l/s of the heated floor area no less than 0.3 l/s of the floor area no less than 0.3 l/s of the floor area 20 l/s 15 l/s 10 l/s

From this table, it can easily be seen that ventilation rate determination is related to either the floor area of a dwelling, the whole house or the habitable space, the number of bedrooms or the type of room. Other aspects are also relevant and

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2.3 Performance parameters related to indoor air quality 17 important, like differences in supply/ exhaust, supply air flow distribution, and supply air quality, these are discussed with other aspects in the text below.

b. supply/ exhaust ventilation

Air supply and exhaust ventilation regulations are in agreement among the 4 countries, all the regulatory standards define that air needs to be supplied to the habitable rooms and exhausted from wet/ polluting rooms, such as kitchens, bathrooms and toilets.

c. whole house/ room level flow rates

In the regulations and standards mentioned above for the 4 countries, either the whole house ventilation flow rates or room level ventilation flow rates are defined, and in some regulations both rates are defined. Furthermore, there are quite some differences among the 4 countries when it comes to identifying the air flow rates for rooms and whole houses, including different definitions or calculation method for habitable spaces, different whole house ventilation requirements, and ventilation determination methods, and different air supply methods.

The methods for determining the room level ventilation flow rates are introduced as:

• in the Netherlands, the building regulation, Bouwbesluit 2003, defines the habitable space as occupation space, ‘verblijfsgebied’ in Dutch, occupation room, ‘verblijfsruimte’ in Dutch. Wet/ polluting rooms typically include kitchens, boiler rooms, bathrooms and toilets. In order to determine the required air flow rates for a domestic ventilation system, first the single occupational room flow rates need to be determined related to the room area, for example, an air flow rate of 0.9 l/s per m2; for two or more connected rooms, i.e. connected through one air flow path, the air flow rate of one of the rooms may be reduced to 0.7 l/s per m2 while the average total air flow rate for these rooms should not be less than 0.9 l/s per m2. The room exhaust air flow rates in kitchens, boiler rooms, bathrooms and toilets should not be less than 21 l/s, 14 l/s and 7 l/s respectively.

• in the UK, indoor domestic space is separated into kitchens, utility rooms, bathrooms, sanitary accommodations and habitable spaces, including

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bedrooms and living rooms. To determine the room level air flow rates, UK building regulation, i.e. building regulation: approved document F, only specifies the total supply air flow for the inhabitable space in a dwelling related to the number of bedrooms but not for each habitable room. Minimum exhaust rates for continuous exhaust or intermittent exhaust are both given for all types of wet rooms.

• in Canada, indoor domestic spaces requiring ventilation are separated into two space categories, i.e. category A which includes bedrooms, basements, living rooms, dining rooms, family rooms, recreation rooms and other habitable rooms, and category B which includes wet rooms, such as kitchens, bathrooms, and laundry and utility rooms. The minimum ventilation air flow rates are given for every room. The exhaust rates from kitchens and bathrooms are given for continuous exhaust or intermittent exhaust. When recirculation air is used, the air flow rates for individual rooms must be revised to meet certain rules.

• in Denmark, the air flow rates are specified for each type of habitable room. A minimum supply air flow rate of 0.3 l/s per m2 of room floor area should be provided.

Once the room level ventilation rates are determined, the whole house ventilation

flow rates must be determined:

• in the Netherlands, the requirement to be used for the whole house ventilation air flow rate is not a fixed value, but should be calculated using the determination method given in the Dutch building regulation. The minimum whole house ventilation flow rate is not the sum of such required individual air flow rates determined by the above described requirements. The whole house ventilation air flow rate is determined by the largest occupation area in the house and normally is not less than the minimum required exhaust rate of 42 l/s. This is because the Dutch building code, Bouwbesluit 2003, requires that there must be the possibility that the occupants of a home can achieve the required air flow rates and it is assumed that the occupants of a home will not occupy all the rooms of that house simultaneously.

• in the UK, whole house ventilation is determined by calculating the total supply air flow rate to the habitable space and the total extract air flow rate

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2.3 Performance parameters related to indoor air quality 19 from the wet rooms. The core of the requirement is to ensure that the total amount of supply air flow rates enter the habitable rooms. The high level of the whole house ventilation rate is at least the greater of the total supply air flow rate and the total exhaust rate, while the low level of the whole house ventilation rate should be not less than the sum of the required supply air flow rates to the habitable rooms. The regulation further specify that the minimum ventilation rate in a domestic setting should not be less than 0.3 l/s per m2 floor area of the whole house with 4 l/s additional ventilation capacity added for each extra occupant.

• in Canada, the minimum whole house ventilation rate is the sum of the required minimum ventilation flow rates in individual rooms or an air change rate per hour (ACH) of 0.3 based on the whole conditioned volume of the dwelling unit.

• in Denmark, the minimum required whole house ventilation flow rates should be no less than the calculated total supply flow rate of 0.3 l/s per m2 of the heated floor area. The high level of the ventilation system should provide a flow rate which is not less than the greater of the total supply flow rate and the total exhaust flow rate.

d. supply air quality: Overflow and Recirculation air

Overflow and recirculation air is the air used for internal air circulation which is not drawn in directly from outside. Overflow air is the air supplied to one habitable room from another habitable room mainly through doors, but not air from wet rooms. Recirculation air is the air extracted by a mechanical system that is returned to the supply duct side of the ventilation system to supply indoor air. In NL and CA regulations, there are options that permit the use of either overflow or recirculation air flow, or both, to supply the indoor ventilation air, such possibilities are not mentioned in the UK and DK regulations.

In NL, the Building Regulation 2003 specifies that at least 50% of the ventilation air should be drawn directly from outside while the rest can be supplied from internal air drawn from other rooms but not wet or polluting rooms, i.e. overflow air (the number of overflow components that the overflow passes should be less than 2) or recirculation air. Recirculation air can be used without an extra air flow requirement.

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In CA, the ventilation standard F326 also provides for the possibility of using recirculation air. If recirculation air is used, the total air flow rates required for air supply or exhaust to/from category A rooms should be increased according to the proportion of the fresh air. Air withdrawn from cooking areas within 1 m from a kitchen device should not be used for recirculation.

The European standard, EN 308, specifies that the rate of the unwanted internal recirculation, i.e. the internal leakage of the heat recovery unit, should not exceed 3% of the total air flow rate.

e. infiltration

Different ventilation standards set different standard for infiltration. Of the 4 countries, only the UK building regulation explicitly allows infiltration to form part of the total ventilation system while in CA, DK and NL infiltration is not to be a part of the ventilation system and should be minimized.

In UK building regulation, recommended ventilation system designs are given based on two different air tightness levels, one in which the assumption is made that there is no infiltration which is suitable for all air tightness levels and another where the assumption is made that there is a background infiltration of 0.15 air changes per hour (ACH) which is suitable for a domestic building when the expected air leakage is higher than 5 m3/h.m2 at 50 Pa.

f. purge ventilation

Purge ventilation requirements are normally met by building windows of the size required in the domestic building regulations of a country.

g. air flow direction

Only Dutch building regulations give clear requirements for indoor air flow directions. In the Dutch building code, Bouwbesluit 2003, it is stated that the air flow direction within a domestic building should be from the habitable rooms to the polluting room such as the kitchens and air flow from a toilet or bathroom to

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2.3 Performance parameters related to indoor air quality 21 inhabitable space should be avoided. Air exhausted from wet rooms should flow directly to the outside of the house.

Additionally, in CA and NL, the regulations specify that air flow resulting from combustion must not be allowed to disperse into the habitable space within a home.

h. supply air distribution

The supply air distribution problem is not well addressed in many ventilation standards, only CA and DK clearly require that supply air should be distributed to individual rooms at a required air flow rate for rooms. This problem is treated differently in the different countries:

• in NL, with a natural supply system, although the air flow rate requirement is given for every habitable space/ room, the regulations do not require the ventilation rates necessarily to be supplied to every habitable space/ room simultaneously. The regulations only require a domestic ventilation system to have the capacity to do this. For a mechanical supply system, the supply air should be distributed to the individual rooms in a home according to the requirements laid out in the regulations.

• in the UK, for a natural supply system, only the whole house supply air flow rate for a natural supply ventilation system is given but not the air flow rates for individual habitable spaces or rooms. For a mechanical supply system, the supply air flow rate should be distributed to an individual room at a ratio of the total supply air flow rate to the whole inhabitable rooms normally in accordance with the ratio of room volume of the individual room to the total volume of all the inhabitable rooms.

• in the CA standard natural supply ventilation systems are not permitted, and the standard requires the required amount of supply air for individual rooms to be delivered simultaneously using a mechanical, ducted ventilation system.

• in DK, the background air exchanges for domestic buildings other than single-family houses should be supplied and exhausted mechanically with heat recovery units.

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2.3.2 Analysis of the required performances in regulations

Key performance parameters

Based on the above review of regulations dealing with domestic ventilation systems in CA, DK, NL and UK, the key performance parameters required in the regulations and standards for a domestic ventilation system related to maintaining an acceptable indoor air quality in a domestic setting are derived as:

• the room exhaust air flow rates

• the room supply air flow rates

• the whole house supply air flow rates

• occurrence of unwanted air flow directions

The key elements used to calculate these performance parameters are defined further below.

Key elements for calculating the key performance parameters

The important elements used to define the performance parameters related to air flow rates are:

• to determine the performance parameters related to air flow rates, 4 issues need to be defined:

(1) the place where the air flow, i.e. exhaust/ supply, should be provided

(2) the operational mode, i.e. the air flow is provided continuously or intermittently

(3) the composition of the air flow should be defined, i.e. how the different segments of air flows must be taken into account, including the ventilation air, the infiltration air, the overflow air and recirculation air

(4) the minimum required air flow rates should be determined. A minimum required capacity is actually not necessary to define a performance parameter, but it is the required value imposed on a performance parameter

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2.3 Performance parameters related to indoor air quality 23

• to determine the occurrence of unwanted air flow directions. The important element here is the definition of unwanted air flow directions, i.e. the air flows from which space to which other space is unwanted.

These two issues are addressed in the generic forms of performance parameters below.

2.3.3 Generic forms of the performance parameters related to air flows We introduce the generic method that can be used to calculate the four performance.

Room exhaust air flow rates

The four key elements, which are discussed below, need to be addressed to determine the performance parameter room exhaust air flow rates..

Spaces requiring exhaust air flows

The regulations on domestic ventilation systems for CA, DK, NL and UK all state that air must be exhausted from wet rooms, i.e. kitchens, bathrooms, toilets, laundry and other polluting rooms, directly to the outside, and not back into the habitable space in a home. Although different definitions of polluting rooms are defined in different countries, minimum exhaust rates with fixed values are given for each type of polluting room in each country.

Ventilation system operational mode

In some countries both continuous exhausting and intermittent exhausting of air are allowed at different capacities, and continuous or intermittent exhausting can be used alternatively or together. Different required minimum air flow capacities need to be defined for different operational modes.

Composition of exhaust air flow

The air flows considered to be exhaust air flow normally only include those flows drawn via the designed air ducts, local fan(s) and natural extraction openings built into the rooms.

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Required minimum exhaust rates

Based on our investigation, we found that for a continuous exhaust system, the required air flow rates range from 13 l/s to 30 l/s in kitchens, 8 l/s to 15 l/s in bathrooms, and 5 l/s to 10 l/s in toilets; intermittent exhaust air flow rates were set at 50 l/s or 60l/s in kitchens and 15 l/s or 25 l/s in bathrooms.

When designing specific domestic ventilation systems for specific cases, the required minimum exhaust capacity of a system can be specified by the designer and be set to meet local relevant regulations. If the required capacity is missing in the local ventilation related code, a reference value from a country or region with homes that have similar room types and usage patterns can be used.

Room/ whole house supply air flow rates

The four key elements need to be addressed to determine the performance parameters, room/ whole house supply air flow rates, are discussed below.

Spaces requiring supply air flows

Ventilation system air flows are normally required to be supplied to the inhabitable spaces within a home, at room level and/ or whole house level.

Operational mode

In most cases, air flows in a domestic ventilation system should be supplied in a continuous mode.

Composition of supply air flow

When considering the supply air quality of a domestic ventilation system, the ideal situation would be that all the supply air is supplied through ventilation openings or other devices directly connected to the external environment but in practice infiltration, overflow and recirculation can play important roles in the supply air. Different countries have different regulations with respect to how much each segment of air flow is allowed to contribute to the total supply air within a domestic ventilation system. The generic equations for calculating the supply air flow rates are given in equation 2.1 and 2.2, and we can manipulate the composition of the calculated supply air flow rates by assigning values to the contribution factors.

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2.3 Performance parameters related to indoor air quality 25 The total supply air flow rate for room (i) or ventilation zone (i) can be expressed using equation 2.1:

, , , , . , . , ,

o tot i vent i ovf i ovf i inf i inf i rec i rec i

q

=

q

+ α

⋅

q

+ α

⋅

q

+ α

⋅

q

_(2.1)

where:

,

vent i

q

_{is the fresh outdoor air flow rate from designed air suppliers for room or}

zone i, including air flow supplied by the ventilation system and window openings, not including infiltration, m3/h

.

ovf i

q

_{is the overflow air rate coming into one room or zone i from another room or}

zone driven naturally, i.e. through internal doors and leaks, m3/h

.

rec i

q is the recirculation air rate coming into room or zone i from the exhausted air flow driven mechanically through the ducts, m3/h

inf,i

q

_{is the air flow rate coming to room or zone i from outside caused by}

infiltration, m3/h

,

ovf i

α

is the contribution factor of overflow air for room or zone i, which can be used as a factor indicating the contribution of the overflow air to the supply air, can be positive or negative depending on the quality of the overflow air, -

,

rec i

α

is the contribution factor for recirculation air of room or zone i, which can be used as a factor indicating the contribution of the recirculation air to the supply air, can be positive or negative depending on the quality of the recirculation air, -

inf,i

α

is the contribution factor for infiltration of room or zone i, which can be used as a factor indicating the contribution of the infiltration to the supply air, can be positive or negative depending on the quality of the infiltration air, -

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The total supply air flow rate for ventilation purpose for the whole house or total inhabitable space can be calculated as:

, , , , ,

o tot o tot i ovf i rec i

i i i

q

=

∑

q

−

∑

q

−

∑

q

(2.2) where: , o tot

q

_{is the total supplied air flow rate for ventilation purpose of the whole house,}

m3/h

Required minimum supply rates

Although in different countries different required air flow rates are used, the underlying ideas are generally related to the number of occupants in rooms and a house and the minimum ventilation air flow rates required for each occupant of a house. It can be concluded from the review in sub-section 2.3.1 that, in general, the minimum ventilation air flow rate for each occupant of a home can vary from 4 dm3/s to 7 dm3/s depending on the country in question and its regulations for domestic ventilation systems.

Similar to the minimum exhaust rates, minimum supply air flow rates for domestic ventilation systems must be determined by the designer according to relevant regulations. If the relevant required values are missing in local ventilation related regulations, a reference value from a country or region with similar room types and usage patterns can be used.

Occurrence of unwanted air flow directions

The air flow direction is an important aspect for the performance of domestic ventilation systems, as air flows in unwanted directions can cause an uncomfortable or poor air quality even when the overall air flow rates are adequately provided in accordance with the regulations. The domestic ventilation regulations in 3 of the 4 countries, CA, DK and NL, specify that unwanted air flow directions should be avoided. Generally speaking, among the regulations for the different countries, the unwanted air flow direction can be specified using the following aspects:

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2.4 Performance parameters related to energy consumption 27

• air flow from combustion appliance or chimney into the habitable space

• back flow crossing the exhaust ducts/ grilles

• reverse air flow crossing the facade air inlets/ outlets

The first 3 aspects listed above should be avoided or minimized in any type of ventilation system. The 4th aspect should be considered according to the system type and its functionality, for example, for a natural cross ventilation system, the air inlets can also be used as air outlets, while in a mechanical exhaust and natural supply system, Dutch standard type, reverse flow crossing the air inlets should be avoided.

2.4 Performance parameters related to energy consumption 2.4.1 Performance parameters in the existing regulations

The required performance for energy consumption are normally not given directly for the ventilation system in the regulations, instead they are given at the whole building level, including energy used by different means, such as heating and lighting. The specific fan power should be below a certain limit, such as 2.5 kW/m3.s, but this is a design rule rather than a performance parameter.

Some standards do give methods that must be used to calculate energy use related to a ventilation system, this is for example done in the EU standards EN 15242 and EN 13790, and through the Dutch standards NEN 8088 and NEN 7120. Though the EU standards and Dutch standards are based on different assumptions, they generally contains the same performance parameters:

• the energy lost due to air exchange

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2.4.2 Determination method of the performance parameters

Key performance parameters

Besides the performance parameters, total energy lost due to air change and fan energy consumption, two more parameters are proposed to be used to define the energy performance of heat recovery systems, i.e. the net energy saved by a heat recovery unit and the overall efficiency of a heat recovery unit. Thus, four key performance parameters are defined:

• energy lost due to air exchange

• fan energy use

• net energy saved by a heat recovery

• global efficiency of heat recovery unit

Methods used to determine each of these four performance parameters are introduced below.

Determination methods for the performance parameters

Hourly total energy loss due to air exchange

We calculate the total energy loss by determining the difference between the energy contained in the exiting air flows and the energy contained in the incoming air flows. The paths for air exchange between a ventilation system, including the ventilation installation and building, and the outdoor air are shown in figure 2.3.

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2.4 Performance parameters related to energy consumption 29

The hourly total energy lost due to air exchange can be calculated as:

, , , , ( ) loss ex i ex i su i su i i Q =

∑

ρc q θ −q θ (2.3) where: loss

Q is the total energy loss due to air change during the calculation hour, kJ

ρ

is air density, kg/m3

cis specific heat of air, kJ/kg.K, is around 1.01 kJ/kg.K under 20 oC

,

ex i

q

_/

q

_{su i}_, _{is the amount of air exhausted/ supplied of certain element (i) of air}

flows during the calculation hour, m3

,

ex i

θ

/

θ

su i, is the temperature of the air exhausted/ supplied of certain segment (i) of

air flow during the calculation hour, oC or K

Hourly total energy used by fans

The performance parameter for the amount of electricity used per hour by a fan can be calculated using equation (2.4).

, , , fan i fan i fan i V P Q = ⋅ ∆ η (2.4) where: , fan i

Q

_{is the electricity used by fan (i) during the calculation hour, J}

,

fan i

V

_{is the volume of air flow across the fan (i)during the calculation hour, m}3

P

∆

is the pressure drop of the whole system during the calculation hour, Pa

,

fan i

η

is the fan efficiency of fan (i), %

Hourly net energy saved by the heat recovery unit(s)

The net energy saved by heat recovery unit(s) can be found in various literature, for example, Schild et al (2003,) which equals the net energy saved by the heat

Method to assess the performance of domestic ventilation systems considering the influence of uncertainties